Caption: Coloured scanning electron micrograph (SEM) Macaw parrot feather rachis (shaft), barbs, barbules and barbule hooks (Ara ararauna). A feather consists of a central axis or rachis, continuous with the hollow quill attached to the bird's body. The rachis bears the flat vane of the feather which is made up of many slender barbs bearing barbules along each side. The barbules of adjacent barbs interlock to form a continuous surface. Magnification: x33 when shortest axis printed at 25 millimetres.